1. Technical Field
The present invention relates to a timepiece mainspring, a timepiece drive device, a timepiece movement, a timepiece, and a manufacturing method of a timepiece mainspring.
2. Related Art
In a mechanical timepiece, as a power source, a power device is generally used which includes a barrel and a mainspring accommodated inside the barrel (for example, refer to JP-A-2009-300439).
In the mainspring of JP-A-2009-300439, in a free state, an inner end side thereof fixed to a barrel arbor is wound approximately 1.5 times in a helical shape.
In a state where the mainspring as in JP-A-2009-300439 is accommodated inside the barrel, the inner end of the mainspring is fixed to the barrel arbor. The mainspring is wound around the barrel arbor, and an outer end thereof engages with an inner wall of the barrel. When the timepiece is used, winding and unwinding of the mainspring are repeated. Here, compared to other portions, in a helical portion on the inner end side of the mainspring, a displacement amount increases due to the winding and unwinding.
In the mainspring in the related art as in JP-A-2009-300439, the helical portion on the inner end side is generally formed in a shape which is plastically deformed if the mainspring is wound. Therefore, after the mainspring is accommodated inside the barrel and wound, durability is degraded compared to that before the mainspring is wound.
For these reasons, there is a problem in that the helical portion on the inner end side of the mainspring is likely to have fatigue failure.